Numerical Simulation of Transient Unloading Response Mechanism of Deep Tunnel Excavation with Single Joint

Using particle flow numerical simulation to reproduce the transient unloading process of a deep buried single joint tunnel, this study explores the influence of crack characteristics on the transient unloading effect of the access tunnel of Shuangjiangkou Hydropower Station from multiple perspectives such as stress state, deformation characteristics and crack propagation. The study shows that the cracks have an important impact on the stress adjustment process of transient unloading in deep buried tunnels, and the stress concentration area will be transferred from the bottom corner of the chamber and the arch to the tip of the crack. As the length of the crack increases, the distance between the stress concentration area at the crack tip and the free surface gradually increases, and the damage area of the surrounding rock gradually migrates towards the deeper part of the rock mass. There is a significant difference in the number of microcracks under different fracture angles, with more microcracks in the 60 ° and 30 ° fractured surrounding rock. In addition, the proportion of compression shear cracks shows a trend of first increasing and then decreasing with the increase of crack angle, and reaches its maximum value at 45 °.The research results have guiding significance for understanding and evaluating the failure mechanism of surrounding rock under the unloading action of hydraulic tunnel excavation.